Storage systems for storing data by using a storage device such as a hard disk drive (HDD) are used. Some of these storage systems include a plurality of physical nodes (also called storage nodes) at which storage devices are provided, and the storage nodes are connected to each other via a network. The storage node is, for example, a computer. Such a storage system may provide the redundancy of data so as to improve fault tolerance by storing the same data in different storage nodes. At that time, it is preferable that data stored in a certain storage node and corresponding data stored in another storage node be the same (be synchronized) after data updating.
A system that includes a local storage and a plurality of remote storages and synchronizes these storages with a time-stamped bitmap has been proposed. Furthermore, a system has been proposed in which a host usually writes data in both a main storage and a sub-storage, and, at the time of occurrence of a failure, a data update history (journal) is transmitted between these storages, not via the host, for the synchronization of the pieces of data. Still furthermore, a system has been proposed in which, when a plurality of logical volumes are copied between storages over a plurality of communication lines (physical paths), a management computer manages the relationship between a physical path and a logical volume and identifies the effect of a failure at a physical path.
Japanese Laid-open Patent Publication No. 2004-272884, Japanese Laid-open Patent Publication No. 2007-86972, and Japanese Laid-open Patent Publication No. 2010-113559 disclose related techniques.